The present nonprovisional application claims priority under 35 USC 119 to Japanese Patent Application No. 2002-0170787 filed on Jun. 12, 2002 the entire contents thereof is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a main wing structure having a particular laminar-flow airfoil and including at least a leading edge structure and a wing central structure coupled to each other.
2. Description of the Related Art
A boundary layer on a surface of a main wing of an airplane is a laminar-flow boundary layer at a leading edge, but changes from the laminar-flow boundary layer to a turbulent-flow boundary layer toward a trailing edge. A friction drag on the surface of the main wing is smaller at the laminar-flow boundary layer than at the turbulent-flow boundary layer. For this reason, in order to decrease the drag on the main wing, it is desirable that a transition point at which the laminar-flow boundary layer changes to the turbulent-flow boundary flow is displaced toward the trailing edge, to thereby extend the region of the laminar-flow boundary layer as much as possible.
A laminar-flow airfoil of xe2x80x9c6-seriesxe2x80x9d developed by NACA in early 1940s can suppress the drag better than the conventional laminar-flow airfoil. However, when a portion of a wing surface in the vicinity of a leading edge is rough, the largest lift disadvantageously tends to decrease largely, leading to a great problem during takeoff or landing of the airplane.
Thereafter, NASA developed NLF(1)-0215F and NLF(1)-0414F in 1977 and 1983, respectively. These laminar-flow airfoils enables a reduction in the drag, but have a problem of causing a large head-lowering pitching moment. Moreover, because these laminar-flow airfoils are for use in a low-speed range, they have a problem of causing drag-divergence phenomenon at an early stage, of a subsonic speed range.
In HSNLF (1)-0213 developed by NASA in 1984 for use in a high subsonic speed range, a drag-divergence phenomenon is difficult to generate, and a head-lowering pitching moment is small. However, the largest lift in a lower Reynolds number range is small and the capacity of an inner-wing fuel tank is insufficient because the wing thickness is about 13% of a wing chord length, leading to a difficulty in ensuring mileage.
A main wing structure of an airplane is constructed from at least a leading edge structure and a wing central structure coupled to each other. Each structure is assembled separately in advance. It is conventionally unavoidable that a small gap and a small step generated between the coupled portions cause an increase in drag. The laminar-flow airfoil is formed to provide a decrease in drag, which is one of its main objects, and hence it is desired that the increase in drag due to the small gap and the small step generated between the coupled portions is minimized.
Accordingly, it is an object of the present invention to minimize an increase in drag due to a small gap and a small step generated between coupled portions between a leading edge structure and a wing central structure, in a main wing structure having a particular laminar-flow airfoil and including at least a leading edge structure and a wing central structure coupled to each other.
To achieve the above object, according to the present invention, there is provided a main wing structure comprising at least a leading edge structure and a wing central structure coupled to each other, wherein said main wing structure has a laminar-flow airfoil comprising an upper wing surface, a lower wing surface, a leading edge and a trailing edge, said upper wing surface including: a front profile portion which has a positive curvature radius, and which is provided to extend from the leading edge to a largest-thickness point located in a range of 30% to 50% of a wing chord length; a central profile portion which has a positive curvature radius, and which is provided to extend from the largest-thickness point to the vicinity of a position corresponding to approximately 90% of the wing chord length at which a value obtained by dividing a thicknesswise difference between the position and the largest-thickness point by a distance in a direction of a wing chord from the largest-thickness point is equal to or smaller than 0.12; and a rear profile portion which has a negative curvature radius or is rectilinear, and which is provided to extend from the vicinity of a position corresponding to approximately 95% of the wing chord length to the trailing edge and wherein coupled portions between said leading edge structure and said wing central structure are arranged at positions corresponding to approximately 20% of the wing chord length.
With the above arrangement, the largest-thickness point at a rear end of the front profile portion on the upper wing surface of the laminar-flow airfoil of the main structure is established at a position which corresponds to a range of 30% to 50% of the wing chord length and which is closer to the leading edge than in the conventional laminar-flow airfoil. Therefore, the pressure gradient in the central profile portion extending from the largest-thickness point toward the trailing edge is gentler than that in the conventional laminar-flow airfoil, thereby stabilizing a turbulent-flow boundary layer and suppressing the occurrence of the undesirable turbulent-flow boundary layer separation to achieve an increase in lift and a decrease in drag. In addition, the rear profile portion which has the negative curvature radius (or which is rectilinear) is provided to extend from the position corresponding to 95% of the wing chord length on the upper wing surface to the trailing edge, thereby suddenly reducing the speed of air flow at the rear profile portion, to positively promote the turbulent-flow boundary layer separation. As a result, it is possible to decrease the lift in the vicinity of the trailing edge of the laminar-flow airfoil, to thereby decrease the head-lowering pitching moment.
In the main wing structure using the laminar-flow airfoil having the above-described characteristic, the coupled portions between the leading edge structure and the wing central structure are arranged at the positions corresponding to approximately 20% of the wing chord length. Therefore, an increase in drag due to a gap and a step between the coupled portions can be minimized, which can contribute to a reduction in fuel consumption.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.